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multistory building and outside plant environments is generally
sized in a tree topology as illustrated in Figure 16.
Determination of cable sizing is initiated at the far end of the
cable route and the backbone cable size increases as users are
added en route to the point of origination, such as the telephone
closet on the top floor of the building.  When feasible, such as
in smaller buildings, it is preferable to run dedicated backbone
cables to each telecommunications closet without splicing.
Single mode fiber optic cable, which is specified for
the outside backbone, will support trunking of voice circuits to
the building either as inter-switch trunks or multiplexed lines.
Data Backbone Cable Requirements.  The variety of data
distribution media (UTP, STP, fiber optic, coaxial), network
topologies, and data rates make determination of a data backbone
system more complicated than for voice.  The RCDD needs to
closely coordinate with the claimant organization to determine
what type of network topology and transmission media is required
to meet the user's short-term (up to 3 years) and long-term (3 to
10 years) requirements.  Topology requirements and distribution
media selection are primarily driven by the electronics
interface/systems selected by the claimant organization.  In a
new construction environment, where determination of claimant
organization (or multiple organizations) requirements are not
fully realized, the installation of multistrand (a minimum of 24
strands) fiber optic cable between each floor and the main
distribution point should meet most short-term connectivity
requirements.  EIA/TIA 568, Section 5 defines the prevalent
topologies used in the data community as the star and ring
topologies (see Figure 16).  IEEE 802.3, Information Technology -
Local and Metropolitan Area Networks - Part 3:  Carrier Sense
Multiple Access With Collision Detection (CSMA/CD) Access Method
and Physical Layer Specifications and IEEE 802.5, Information
Technology - Local and Metropolitan Area Networks - Part 5:
Token Ring Access Method and Physical Layer Specifications
further define data topologies.  Backbone distribution for data
connectivity is provided between the main distribution location
and each telecommunication distribution closet or between
buildings in the campus distribution environment.  EIA/TIA-568,
Figure 5-5 delineates distance limitations recommended for each
of the distribution media types.  UTP cable is not designed or
recommended for inter-building backbone application.  It is
recommended that single mode fiber be used for inter-building
backbone applications.  When possible, for physical protection
and administrative ease, it is recommended that separate voice
and data backbone pathways be used.  It is recommended that fiber
optic cable be routed in an innerduct when backbone pathways must
be shared.  A single innerduct should never be pulled into an

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